Between astro labs, outreach and personal viewing I use mine quite a bit. A lot of use is with an Orion Photographic SkyGlow filter. In a 70mm f/4 refactor working at f/2 we saw nebulosity around the Pleiades from the University observatory parking lot. At the edge of a small city there is quite a bit of light pollution. This filter works great on globulars, open clusters and about anything that I don't use the Ha filter with. Scintillation is minimized with the Orion filter also.

Two years ago I attended a star party that featured a "Mallincam Row". Behind a low hill were several guys with EQ mounts, batteries, big monitors, etc. I got to talking with a friendly guy building up a nice image of M27. With the focal length of a 10-in scope the Dumbell nearly filled the screen. When he had a spare momnent I asked if he wanted to take a look at the North American Nebula. He said it was too big for his camera. I handed him an 80mm f/3.7 achro with my IIE, focal reducer and Ha filter and told him to take a look. You could almost hear his jaw drop. Within a few minutes most of the other imagers had to look. Before the night was over I found another guy witha 10-in f/4.9 dob that would allow the IIE to reach focus. Soon there was a line of folks waiting to see the HorseHead, most for the first time

About 3 or 4 years ago I did a comparison of 3 different Ha filters. This was done on a clear and transparrent night on a mountain at around 6000 ft. I am going from memory as I can't find my notes. The target for comparison was the North American Neb. The scope was my trusty 80mm f/3.7 with a .6 focal reducer. All observations were with the scope hand held. Two of the filters came from the local University observatory. IIRC they were 4.5nm and 10nm. I also had a new 14nm I had just purchased.

Several times over the course of 45 minutes I switched from filter to filter, trying to determine if one was "better" than the other 2. The most contrast was seen with the 4.5nm. The faintest details were seen with the 14nm. Th 10nm seemed a good compromise. I already owned the 14nm but if I were to buy another one it would be in the 9-10nm range.

One factor which might contribute to the seemingly poorer performance of a narrower bandpass is the steepness of the light cone. An f/3.7 reduced by 0.6X is awfully steep, and can result in 'detuning' of light passing through the edge zone of the objective. The result is effectively a domewhat smaller working aperture at the desired wavelength.

In order to employ the narrower bandpass filters efficiently, place them in the beam where the rays are not so strongly converging toward focus. This can be ahead of a reducer, or better yet--if the filter is large enough(!)--ahead of the objective.

For example, I recall my Baader 7nm H-alpha instruction sheet stating that it's recommended to go no faster than either f/2.8 or f/2.5 (can't recall exactly at the moment.)

I'm not educated or smart enough to get into details where the filter works best with a fast light cone. I'm a "try it and see what works" kind of amateur astronomer. I do know that if the focal reducer is put in front of the Ha filter focal reduction is too severe and the image degrades, especially at the edges. So the focal reducer screws into the IIE barrel first and the Ha filter goes in front of it. The 70mm working at f/2 does very good. The 80mm working at f/1.9 "pops" the nebs more. Then again a 15-in f/5 dob working at f/3 is astounding for fainter and smaller stuff. My 8-in f/4 ain't too shabby either.

Back in March '08 I observed in a very dark and clear sky and saw the Meissa Ring in Orion (among many other objects) with a 62mm f/5 achro and .6 focal reducer. Lotsa fun!

Looks like there are not nearly as many observers with IIEs as folks with cams. A year or so ago I was at a star party for 3 nights. A lot of attendees, maybe over 100. The morning I left I found out there was a guy there with a BIPH. Wish we had met up as I have always wanted to see one of those in action.

Oddly, a lot of amateur astronomers seem unaware of the potentential of IIEs. They hear "Oh, those things are so expensive" or "All you see is green and you lose your night vision" and they lose interest. But it is interesting to see the looks on their faces if they view through my IIE at some target that is barely a smudge or even invisible in their own expensive set up. Like any other tool you learn to maximise it's use.

Of course the cost limits the size of our "club". But looking at the price of some modern premium eyepieces, cameras and other astro goodies the price of a used Collins I3 or BIPH seems not so bad. Occasionally there is an ad on Ebay for a gently used basic monocular or riflescope with a Gen II or Gen III heart. Last year I saw a Gen III one that sold for less than $1500. A decent ATM could convert one of these to astro use.

For 25 years I observed frequently with my own scopes. Refractors up to 5 inches and newts up to 8 inches. Of course I viewed through many bigger scopes owned by others. After a while, viewing the same DSOs over and over was starting to get boring and definitely was getting more challenging due to increased light pollution. The IIE opened up a new world of observational astronomy. Non solar system objects that were difficult were now easy. Many objects that I had never even seen before were within my grasp with modest sized equipment. Five years ago I crossed over to the "green side" and have no regrets at all.

I am still observing with my BIPH (gen 3 intensified binoviewer) whenever I get the chance. I most recently observed 2 rather faint emission nebulae --- the Elephant's Trunk in Cepheus and Simeis 57 in Cygnus. I used the BIPH on my homebuilt 18.5" F4.0 Dob with a 7nm Baader HA filter and a focal reducer (my scope was working at about F2.5).

The black outline of the Elephant's Trunk was distinctly visible for the entire length --- it looked to me much like the Pillars of Creation in M16. I observed in my 5.5 mag backyard and a local darker site about 6.1 mag. The contrast in the trunk was better at the darker site but was still easily visible from my backyard.

In Simeis 57 (nickname the Propeller Nebula) I could easily observe the 2 main propellers. In fact, I also observed 2 fainter propellers on each side that formed a figure 8 that were not on the photo I originally used to find the object. I checked on-line and saw the 2 fainter propellers on a longer exposure image exactly where I observed them in the BIPH. I believe this was a 2+ hour exposure and I was able to see all 4 propellers with my BIPH in real-time -- in my backyard!

I wrote a more detailed "BIPH Observing Report" on Cloudy Nights about 2 years ago after I observed at a very dark sky site ---here is the link:

My favorite ii experence has been using my super portable/simple C5 w/the f6.3FR and BIPH (and/or 135mm cameral lens for wide angle sweeps), both w/Ha filter. Rarely see dark skies here at home but this stuff travels and sets up so quickly and easily everywhere I go its a piece of cake and excites everyone who looks...including the grandkids.